Minnesota Construction Specification 214—Cathodic Protection for Buried Metal Structures

1.Scope

The work shall consist of furnishing and installing all material necessary to provide cathodic protection for metal structures as shown on the drawings.

2.Materialspecification

Anodes and connections shall conform to the requirements of Material Specification MN-306.

3.Installing anodes

The anode metal shall be centered in the packaged backfill just prior to installation. Anodes may be placed either horizontally or vertically and shall be deep enough to have at least three (3) feet of earth cover. Unless otherwise specified the anodes shall be saturated with a minimum of five (5) gallons of water after being placed, and prior to being backfilled. Moist, fine-grained earth material shall be used to backfill around the anodes. Compaction shall be to the density of the surrounding fill and shall be accomplished by means of hand tamping or manually directed power tampers or plate vibrators. The fill shall be placed in layers not exceeding four (4) inches prior to compaction.

4.Attaching anode to pipe

The lead wire from the pipe shall be attached to the pipeline by a powder welding process. The area of damaged pipe coating and the weld shall be repaired as specified in Section 6.

Unless otherwise specified, the lead wires from anodes shall be connected to the header wire by a powder weld, brazed or silver soldered. The connection shall be made waterproof and tightly wrapped to a minimum thickness of 24 mils of vinyl plastic electrical tape. Prior to wrapping, the connection shall be thoroughly cleaned to remove all foreign material and moisture.

5.Testing stations

A testing station shall be installed as shown on the drawings for each anode bed installation. The anode lead or header cable from the anode bed and the lead wire from the pipeline shall be placed in a galvanized metal conduit between the ground surface and the test box.

The test box shall be a metal, weatherproof device. The leads shall be connected to a terminal post or block or be connected with a split bolt connector. The electrical circuit shall be insulated from the test box.

6.Repair of damaged coatings

Any damage to the zinc coating shall be repaired by thoroughly wire brushing the damaged area, removing all loose and cracked coating, removing all dirt and greasy material with solvent, and painting with two coats of zinc dust-zinc oxide primer conforming to the requirements of Federal Specification TT-P-641, Type III, or zinc dust paint conforming to the requirements of Military Specification MIL-P-21035. If the coating is damaged in any individual area larger than 12 square inches or if more than 0.2 percent of a total surface area of a length of pipe is damaged, the length will be rejected.

Bituminous coating damaged by welding or breaks or scuffs in bituminous coatings that are less than 36 square inches in area shall be repaired by the application of two coats of hot asphaltic paint or a coating of cold-applied bituminous mastic. The repair coating shall be at least 0.05 inches thick after hardening and shall bond securely and permanently to the connection and the pipe. The material shall meet the physical requirements for bituminous coatings contained in the references cited in Material Specifications 551 and 552. Whenever individual breaks exceed 36 square inches in area or when the total area of breaks exceeds 0.5 percent of the total surface area of the pipe, the pipe will be rejected.

Polymeric or pitch resin coating damaged by welding of coated pipe or pipe fittings and breaks or scuffs in polymeric or pitch resin coating that are less than 36 square inches in area shall be repaired according to the manufacturers recommended repair procedure. Surfaces to be coated must be clean and dry. The repair coating shall be at least 0.010 inches thick after hardening and shall bond securely and permanently to the pipe. The material shall meet the physical requirements for polymeric or pitch resin coatings contained in the references cited in Material Specifications 551 and 552. A plastic or vinyl repair coating shall be similar and equal in quality to Scotch-Clad Protective Coating 1706, manufactured by 3M Co., 3M Center, St. Paul, Minnesota. If the repair coating thickness is not measured, six coats shall be applied allowing 30 minutes drying time between coats. Whenever individual breaks exceed 36 square inches in the area or when the total area of breaks exceeds 0.5 percent of the total surface area of the pipe, the pipe will be rejected.

7.Constructiondetails

NRCS-Minnesota(210-VI-NEH May 2005)MN214-1